This is half life. you cant change its main character that define the game. thats my point.
its like making tomb raider not starting lara croft.
Well, technically you could have a Tomb Raider game without Lara Croft. It would be iffy, but I'm sure there's more than one 'tomb raider' in the setting.
But they're not quite equivalent. Lara Croft has starred in every Tomb Raider game. Gordon hasn't starred in every Half-Life game, and that became the case as soon as Opposing Force was released.
and Gordon freeman is much better character than Lara "this is soo hard, I cant do this" croft
Again, what is Gordon's personality? What is conveyed in the games themselves?
Freeman is already well established as the main character and it's his journey and should end with him, whether you like him or not. I don't even like mute protagonists and don't think much of Freeman as a character, but replacing him at this point would just be wrong.
Even if we accept Gordon as the main character of the setting (which isn't unreasonable), what has that translated into, story and character-wise? Because Gordon's never developed as a character. And his role in the plot is entirely reactionary. I can't really say he's on a "journey" when that journey has never really translated into anything approaching character growth. Even Chell felt more developed in that stuff about her was hinted at within the game, and there was a more intimate sense of character between her and GLaDOS, even if Chell never talked.
Some silent protagonists can still demonstrate emotion, character arcs, and backstories revealed in the game (e.g. Link and the Doom Slayer), but Gordon fails even at that.